I have this problem, too! In TurboTax, I clicked on, "What if the amount from my letter doesn't match my records?" and then logged into my personal account on the IRS web site as suggested by the TurboTax On Demand Tax Guidance to check my "2021 Advance Child Tax Credit Payments Information." Here's what the IRS directed there:
"If There Are Differences With the Amounts From Your Mailed Letter 6419
Use the information shown on this page when filing your 2021 tax return to avoid any processing delays. The amount on this page is the most accurate information about the advance Child Tax Credit payments."
So, the IRS says ignore the Letter 6419 amounts and use the figures displayed for you on the IRS web site.
